An analysis of surface breakup induced by laser-generated cavitation bubbles in a turbulent liquid jet

Abstract

The breakup of turbulent liquid jets by cavitation bubbles was investigated by artificially introducing them by focusing laser light into the jet. The induced surface deformations and ejected liquid structures were characterized using shadowgraphy with a high-speed video camera. The flow velocity of the liquid jets, which were ejected from a 6 mm nozzle, was varied by adjusting the injection pressure from 1 to 5 bar. Deionized water and a dipropylene glycol–water mixture were used to compare the breakup of liquid jets with different surface tension and viscosity. Surface deformation and breakup were found to occur in two stages. One was early breakup of liquid strings into tiny droplets. This was followed by the formation of a larger structure separating into ligaments and larger drops. Averaged time-resolved one-dimensional plots were introduced and implemented to analyze breakup statistically, to address the problem of shot-to-shot variations in the breakup due to the turbulent condition of the jets. Bubble-induced breakup could easily be distinguished from spontaneous breakup with this method. Both the position of bubble formation and the injection pressure had an influence on the scale of the breakup. The deformation of the jet surface was highly affected by shear. The structure of the deformation became less intact when the surface tension was lower. The sizes of the drops produced during the second stage of breakup were analyzed. The bubble-induced breakup produced smaller drops than the spontaneous breakup at lower injection pressure. As expected, lower surface tension favored droplet detachment and smaller sized drops. Graphic abstract

Numerical and experimental investigation into the dynamics of a bubble-free-surface system

“…The most prominent example is the ocean, where bubbles bursting at the air-sea interface produce sea sprays, which strongly influence the coastal ecosystems and global climate patterns [5][6][7][8][9]. The dynamics of a bubble-free-surface system are also important to many technological applications, such as underwater explosions [10][11][12], printing or deposition techniques [13][14][15], drug delivery systems [16], and liquid fuel injection [17][18][19][20][21]. The bubbles in these applications may be oscillating, often quite violently.…”

Microsecond cell triple-sorting enabled by multiple pulse irradiation of femtosecond laser

“…In other words, for a given femtosecond pulse energy, the impulsive force remains constant. The cavitation detonation increases as the energy of the femtosecond pulse increases, which results in a larger impulsive force 42 – 44 . By increasing the pulse energy from 4 to 20 μJ/pulse, the streamline manipulation success rate increases from 20 to 80%, as shown in Fig.…”

Numerical modeling of droplet rim fragmentation by laser-pulse impact using a multiscale two-fluid approach

“…Further development of the proposed multiscale two-fluid approach to incorporate an AMR algorithm and phase-change phenomena, namely, a cavitation and vaporisation model, will provide a valuable numerical model to investigate a broader range of unsteady fragmentation problems and obtain an insight into the sizes of the produced fragments that is not easily accessible from the experimental observations. Examples of fragmentation cases of interest in the literature to date include the violent laser-induced droplet fragmentation in biofuels [51] and screen printing inks [52], the explosive droplet fragmentation [22] and the surface jet breakup [53] by laser-induced cavitation bubbles and the breakup of laser-induced jets in needle-free medical injections [54], among others. concentrations of fragments using the multiscale two-fluid approach satisfactorily converge in all examined conditions.…”